This invention relates to an apparatus of manufacturing sheets from finely divided material exhibiting a size distribution, such as chips, fibers or the like, especially for the manufacture of wood chip panels, in general and more particularly to an improved method of this type.
A manufacturing method of this general type in which the excessively coarse particles are separated out and a substantially horizontally advancing, a stratified mat is formed from the remaining particles by spraying, in such a manner that the finer particles get to the upper and/or underside of the mat, and in which the stratification is produced by imparting a motion component to the falling particles, which is parallel to the forward direction of the mat and differs depending on the coarseness of the particles and thereby, causes different falling tragectories to be forced thereon, and in which the stratified mat is subsequently subjected to surface pressure, as well as to corresponding apparatus, is known.
The finely divided material used for the manufacture of the sheets does not consist of uniform particles. Rather, all possible sizes of, for instance, chips are represented in accordance with a random distribution within a certain size range. Among them are also chips and pieces of wood which are so large that they would interfere with the desired structure of the sheet. These chips must therefore be sorted out before they get to the mat which is formed by sprinkling on an advancing belt. The material is therefore subjected to a sifting operation, in which the excessively coarse particles are separated out.
Customarily, this sifting operation precedes the spraying process proper. It can consist, for example, of an air separator, in which the particles are allowed to drop onto a conveyor belt from a delivery zone which is situated above the conveyor belt and extends over the entire width of the latter. The dropping particles obtain a motion component parallel to the forward travel direction of the belt by means of an air nozzle arrangement disposed below the delivery zone above the conveyor belt. The lightest particles are deflected farthest by the air and the heaviest particles drop substantially vertically and are deflected hardly at all. In the striking range of these particles, a collecting device is provided which collects and removes the heaviest particles before they get on the conveyor belt which transports the other particles away. From this conveyor belt, the mixture of the lighter particles then goes into the sprinkling device, in which the stratified mat is formed. Other sifting devices are also known.
The initial sifting operation results in substantial additional cost.